Variable pitch marine propeller



Dec. 8, 1959 K. R. MADES VARIABLE PITCH MARINE PROPELLER 6 Sheets-Sheet 1 Filed Aug. 3, 1955 W gas 7 Dec. 8, 1959 Filed Aug. 3, 1955 K. R. MADES 2,916,095

VARIABLE PITCH MARINE PROPELLER j 6 Sheets-Sheet 3 F f if/x T I\ l\ I j/ 19 (52 M A 7 g x\\\ A Dec. 8, 1959 K. R. MADES VARIABLE PITCH MARINE PROPELLER 6 Sheets-Sheet 4 Filed Aug. 3, 1955 Dec. 8, 1959 K. R. MADES VARIABLE PITCH MARINE PROPELLER 6 Sheets-Sheet 5 Filed Aug. 5, 1955 Dec. 8, 1959 K. R. MADES VARIABLE PITCH MARINE PROPELLER 6 Sheets-Sheet 6 Filed Aug. 3, 1955 VARIABLE PITCH MARINE PROPELLER Karl Rudolf Mades, Berlin, Germany Application August 3, 1955, Serial No. 526,281

5 Claims. (Cl. 170-160.34)

Reversible screw propeller installations for ships normally comprise a propeller shaft which is axially displaceable in the fore and aft direction of the ship with respect to a control head which is rotatable with the propeller shaft but not displaceable in the fore and aft direction, the propeller blades having shanks or pivots which are rotatable in a hub fixed to the propeller shaft and the control head having pins thereon which engage slots offset from the axes of the blade pivots and provided in the bases of the blades or in lugs integral with the blades, so that by axially displacing the propeller shaft with respect to the control head the blades are constrained to turn around the axes of their pivots to adjust them for reversing the direction of travel of the ship. It is also known to mount the blades on a hub which is rotatable with the propeller shaft but is immovable in the fore and aft direction, the blades being adjusted by displacing the propeller shaft axially with respect to the said hub.

It has been found that in these knowninstallations the power required for adjusting the blades is consider.- able and in the case of installations in which a large main engine is required for to drive the propeller, the power expended in adjusting the blades is so great that the known blade adjusting mechanisms cannot be employed, the basic reason for this being the friction of the blade pivots in their hearings in the hub. The length of the pivots of the blades has to be kept short owing to .the small radial distance available for their accommodation so that the bearing pressures are con.- siderable. In small power installations the bending moment set up in the blade pivots, due to the thrust applied to the blades during the operation of the propeller, and the friction between the blade pivots and their bearings are not sufficiently great to be overcome by the use of a reversing mechanism of reasonable power and size. In the case of large installations having a main engine of considerable size, however, the forces acting on the pivots of the blades are so considerable that the pivots may even bind in their bearings to such an extent as to be immovable, no matter how powerful the blade adjusting mechanism employed.

The main object of the present invention is to provide a reversible screw propeller installation which can be used in large ships and requiring the minimum of power for effecting the adjustment of the blades.

In the case of a ship under way, the wake current due to the relative motion between the ship and the Water sets up forces which are applied to the propeller blades in such a manner as to produce an axial thrust on the propeller shaft. If, for instance the ship is being driven forwardly it will continue to travel ahead, owing to its momentum, when the main engine is stopped and the wake current will tend to rotate the screw propeller in the same direction of rotation as when propelling the ship and to pull the propeller shaft out of the hull of the ship against the opposition of the main thrust bearing.

According to the present invention the forces produced by the wake current, which are known to be considerable, are utilised to effect or assist the adjustment of the blades of a reversible screw propeller. For this purpose, an axially displaceable propeller shaft is employed and the blades are mounted on a hollow hub fixed to the propeller shaft, the blade pivots extending into the hub and having flanges which are connected by means of links to a control head through which the propeller shaft extends, the said control head being rotatable with the propeller shaft but being immovable axially with respect to the hull of the ship and the said links being so arranged that when the propeller shaft is displaced axially with respect to the control head they will rotate the flanges of the blade pivots and produce angular adjustment of the propeller blades. During normal travel of the ship, the propeller shaft is prevented from being displaced axially by means of an axially adjustable main thrust bearing provided with means comprising a reversible auxiliary engine for adjusting it in the fore and aft direction of the ship to allow the propeller shaft to be displaced axially under the action of the wake current.

In order that the invention may be clearly understood and readily carried into effect, the same will now be described more fully with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic longitudinal section of the rear part of a ship fitted with a reversible screw propeller installation according to the present invention;

Figure 2 is a top plan view on a larger scale of the propeller hub, showing one of the blades in the forward, reverse and feathered positions, respectively;

Figure 3 is a cross-section through the hub of the propeller, the section being taken along the line ;3 3 of Figure 4;

Figure 4 is a vertical longitudinal section through the propeller hub, the section being taken along the line 4--4 of Figure 3;

Figures 5 and 6 are detail sectional views of the blade pivot as shown in Figure 4 with modified forms of pivot bearing;

Figures 7-9 are detail views, partly in longitudinal section, of alternative forms of the thrust bearing shown in Figure 4 for the control head of the blade-adjusting mechanism;

Figure 10 is a diagrammatic sectional view to illustrate the manner in which the propeller hub is removed from the propeller shaft;

Figure 11 is a diagrammatic longitudinal section of the rear part of a ship fitted with a modified form of the reversible screw propeller installation according to the invention;

Figure 12 is a side elevation on a larger scale, partly in central longitudinal section on the line 1 2 -,12 of Figure 15, of the propeller hub shown in Figure 11;

Figure 13 is a side elevation, partly in central longitudinal section, of the main thrust bearing of the installation shown in Figure 11;

Figure 14 is a detail cross-section along the line 1414 of Figure 13, and

Figure 15 is a cross-section through the propeller hub along the line 1515 of Figure 12.

Referring to Figs. 1 to 4, the screw propeller installation illustrated comprises a propeller shaft8 which is rotatable and axially displaceable in the stern tube 10 of the ship, the stern tube being provided with a conventional gland 13. The propeller shaft 8 passes out of thestern of the ship through the A-frame 9 and exten s into a hollow two-part propeller hub 14, 15 below the ,water line 11. As shown in Fig. 1, the propeller shaft Skis driven by the main engine 1 of the ship, the driving shaft 121 of theengine ,1 being presided with acoupling member 2 having a hollow enlarged portion 122 into which the forward end of the propeller shaft extends. The forward end of the propeller shaft is provided with clutch teeth 124 which engage internal clutch teeth 125 on the enlarged portion 122 of the coupling member 2, thereby furnishing a positive driving connection between the engine driving shaft 121 and the propeller shaft 8, while permitting the propeller shaft to be displaced axially.

For the purpose of resisting axial displacement of the propeller shaft 8, an adjustable main thrust bearing 4 is arranged rearwardly of the coupling member 2, the said thrust bearing being in engagement with a thrust collar 126 integral with the shaft 8. The thrust bearing '4 is adapted to be displaced in the fore and aft direction of the ship by means of an adjusting device comprising a reverisble auxiliary engine 7, on the driving shaft 161 of which are fixed a pair of worms 162 in engagement with Worm wheels 6 fixed on screw spindles which extend parallel to the shaft 8 and are inserted into screw-threaded openings in diametrically opposed lugs 127 integral with the thrust bearing 4.

The rear end of the propeller shaft 8 has a tapered portion 27 which is inserted through a tapered opening in the rear end of the after part 14 of the propeller hub, the shaft 8 being secured to the part 14 of the hub by means of a nut 16. The portion 27 of the shaft 8 has a taper of 1 in 10, ensuring a firm seating of the shaft while enabling the propeller hub to be readily withdrawn from the shaft by means of any known type of draw-off device. The shaft 8 is prevented from rotating relatively to the propeller hub by means of a key 271 which engages in a keyway formed in the wall of the tapered opening of the hub part 14. The two parts 14, 15 of the propeller hub are secured to one another by means of internal screw bolts 25 which are passed through holes in the part 14 and are screwed into lugs 251 integral with the part 15. The nut 16 and the heads of the bolts 25 are enclosed within a streamlined hub cap 17 which is removably attached to the rear end of the propeller hub.

The propeller hub 14, 15 is provided with circumferentially spaced bearing openings 141 to receive the pivots 26 of screw blades 18, three of which are provided in the embodiment illustrated, the said openings tapering inwardly and the pivots 26 being correspondingly tapered. The blade pivots 26 extend through the openings 141 into the propeller hub and are maintained in position in the said openings by means of circular flanges 29 integral with the inner ends of the pivots 26 and in contact with bearing surfaces on the inner side of the wall of the hub surrounding the inner ends of the openings 141. The joint between the parts 14 and 15 of the propeller hub extends in a plane containing the axes of rotation of the blade pivots 26, so that the pivots can be inserted into and removed from the openings 141 after the part 14 has been separated from the part 15. The undersides of the flanges 29 are in contact with flat bearing surfaces 221 on a triangular section control head 22 having an axial opening through which the propeller shaft 8 extends.

The blade pivots 26 and the bearing openings 141 have a taper of 1 in 4 so that the blade pivots are not liable to become wedged in the openings 141 and such wedging, which would be liable to cause seizure of the pivots in the bearing openings, is prevented by the action of centrifugal force which tends to displace the pivots 26 radially outwards during the rotation of the propeller. Furthermore, owing to the flanges 29 of the blade pivots being located between the bearing surfaces on the inner wall of the propeller hub and the hearing surfaces on the control head 22, the blades 18 are supported in such a manner as to preclude any tilting of the pivots due to the bending moments produced by the axial thrust acting on the blades during the rotation of the propeller. The blades are thus w'ell supported and guided in the hub in spite of the shortness of the blade pivots due to the limited amount of radial space available for the accommodation of the pivots.

The control head 22 is rotatable around the axis of the propeller shaft 8 but is prevented from displacement in the fore and aft direction of the ship, being provided with a self-aligning roller thrust bearing 34, the inner race 134 of which is fixed on a tapered shank portion 321 of the control head, while the outer race 135 is fixed in an enlarged part of a retaining sleeve 136 encircling the shaft 8 and secured to the stern of the ship, extending into the A-frame 9 where it is secured against axial displacement by means of a collar 137 (Fig. 1) which engages in a recess in the A-frame 9. As the thrust bearing 34 is arranged outside the ships hull it also serves as the stern bearing of the propeller shaft, and owing to the bearing 34 being of the self-aligning type it is uniformly and centrally loaded.

Owing to the flanges 29 of the blade pivots being in close contact with the bearing surfaces on the inner wall of the propeller hub and with the flat bearing surfaces 221 of the control head 22, they act as driving members constraining the control head to rotate with the propeller shaft 8, the thrust bearing 34, however, preventing the control head from following any axial displacement of the propeller shaft, which is freely slidable in the axial opening of the control head.

The blades 18 are adjusted by means of links 19 connected to the control head 22 by means of pivot pins 21 on the control head and to the flanges 29 of the respective blade pivots by means of crank pins 20. When the blades 18 are positioned for driving the ship forwardly, the propeller hub 14, 15 is located in its extreme forward position as shown in full lines in Fig. 2, the pivot pins on the control head being offset laterally from the axes of rotation of the blade pivots and the crank pins 20 being so located on the flanges 29 that the links 19 extend perpendicularly to the axis of the propeller shaft. Each flange 29 has a peripheral slot 191 therein through which its crank pin 20 extends, the links 19 extending into the slots 191 of the respective flanges 19. In Fig. 2 the blade 18 is shown in crosssection at two thirds the radial distance from the axis of the propeller shaft to the tip of the blade, E being the leading edge, A the trailing edge, D the pressure side and S the suction side of the blade.

Except when it is required to adjust the blades 18, the main thrust bearing 4 is stationary and prevents the propeller shaft 8 from being displaced axially by the wake current. When it is required to adjust the blades, the main engine is stopped or uncoupled from the propeller shaft and the auxiliary engine 7 is started up to adjust the thrust bearing fore and aft in the direction required to enable the propeller shaft to be displaced axially by the thrust of the wake current acting on the blades 18. When the blades 18 have been adjusted into the required position the auxiliary engine 7 is stopped and the main engine is started up again or coupled to the propeller shaft. Owing to the axial displacement of the shaft 8 with respect to the control head 22, the links 19 constrain the flanges 29 of the blade pivots to rotate and thereby angularly adjust the blades 18. Thus, in order to enable the blades to be adjusted from the. full ahead position shown in full lines in Fig. 2 to the full astern position 18 shown in broken lines, the engine 7 is operated to displace the thrust bearing 4 towards the stern of the ship through the worms 161, the worm wheels 6 and the screw spindles 5, thereby allowing the propeller shaft to slide rearwardly through the control head 22 under the action of the wake current.

In reversible screw propeller installations, angular adjustment of the blades from the full ahead to the full astern position amounts usually only to about.45. For

setting the blades from the full ahead position through 'efjf ull' astern position into the feathering position 18 in Fig; 2, this being the position of the blade 18 shown in Fig. 4, an angular adjustment of at least 105 is required. Such a large angular adjustment could not be achieved by the methods hitherto known, without unsuitable angles occurring in the end positions between the linksand the crank radii. In the present case, as the links 19 he perpendicularly to the axis of the propellershaft when the blades 18 are in the full ahead position, during the initial displacement of the propeller shaft for adjusting the blades to drive the ship rearward-1y the links 19 are substantially tangential to the circular paths a of the centres of the respective crank ins 20. The links 19 are thereby able to apply the torque to the flanges 29 of the blade pivots at the commencement of the angular adjustment of the blades from the full ahead position. Moreover, during initial part of the said displacement of the propeller shaft only a comparatively small angular adjustment of the blades is eifected for an appreciable axial displacement of the propeller shaft, thereby enabling the blades to be set precisely to the required position for forward travel of the ship. Moreover, owing to this arrangement of the links 19 there is almost no axial pressure on the control head 22 when the blades are set for forward propulsion, the setting which they occupy during the major part of the time the propeller is in operation. When the blades have been adjusted to the full astern position 18 the links 19 occupy the position shown in broken lines, in which position they are also substantially tangential to, the circular paths a of the centres of the crank pins 20. In order to enable the blades to be adjusted into the feathering position, the propellet shaft 8 is allowed to be displaced rearwardly by the wake current beyond the position corresponding to the full astern position of the blades, the flanges 29 of the blade pivots rolling on the crank pins 20 while the links 19 do not move appreciably from the position shown in broken lines, until the crank pins have rotated through .60 from the position they occupy when the blades are in the full astern position. The blade adjusting mechanism described thus does not oppose any appreciable resistance to axial displacement of the propeller shaft by the wake current for adjusting the blades from the full ahead to the full astern and feathered positions, or in the reverse direction to adjust the blades back again from the full astern to the full ahead position.

I puring the rotation of the screw propeller, the reaction ofthe blades with the water produces an axial thrust. on the blades which forces the blade pivots hard against their bearings in the propeller hub and tends "to wedge them in their bearings, this thrust greatly exceeding that due to the wake current and increasing proportionately with the speed of travel of the ship. For this'reason it has hitherto been necessary to employ a large reversing engine for effecting the blade adjustment, since this engine has to be capable of delivering satficient power to eifect the blade adjustment against the considerable resistance to angular motion of the -duced by the wake current, however, is suflicient to 'effectthe axial displacement of the propeller shaft for adjusting theiblades when the ship is under way. When the speed of the ship is sufliciently reduced, the wake current may notbe sufficient to produce the required blade adjustment alone so that the auxiliary engine 7 willhave to supply some of the power to produce the adjustment. Even when the ship is stationary or nearly stationary, only a comparatively small engine 7 will sufli'ce to produce the necessary axial displacement of the propeller shaft to adjust the blades without assistance from the wake current, since the forces opposing such axial displacement are then negligible, the blades only having to be adjusted against the static resistance of the Water.

When the'blades are in the feathered position, the wake current will tend to prevent axial adjustment of the propeller shaft if the ship is travelling ahead. The blades are only feathered, however, when the ship is taken into tow and is travelling at a comparatively slow Speed and by the time the tow ropes are cast oh and the ship is ready to proceed under its own power it will be practically stationary and it will be possible to adjust the blades from the feathered position through the full astern position to the full ahead position by means of the auxiliary engine alone.

Thus, by means of the blade adjusting mechanism described it is possible to effect all the necessary adjustments of the blades by means of a small powered engine with the assistance of the wake current when the ship is under way. In one reversible screw propeller installation, for instance, having a main engine of 12,000 HP. at 400 r.p.m., a blade-adjusting engine having an output of only 10 HP. has been found to be sufficient for producing the necessary axial adjustment of the main thrust bearing.

Fig. 5 is a detail view showing a blade pivot 26 provided with an antifriction bearing surface 261 and an antifriction bearing ring 262. on the upper face of the flange 29 and Fig. 6 is a similar detail view showing a blade pivot 26 with its flange 29 provided on its upper face with an antifriction bearing ring 262 and on its lower face with a circular antifriction bearing disc 263.

Figs. 7-9 show alternative forms of the thrust bearing for the control head 22, each having an outer race 37 provided with a spherical seating surface. In Fig. 7 the race 37 is of channel section and encloses a row of bearing rollers 31 which cooperate with a flat annular inner race 312 to form a journal bearing element, the axial thrust acting on the control head 22 being taken by bearing balls 32 interposed between the sides of the race 37 and flanges 321 integral with the control head. In Fig. 8 the outer race 36 is provided with two lateral grooves, each accommodating a row of bearing balls which co-operate with arcuate bearing surfaces connecting the shank of the control head and two integral flanges 322 arranged on the opposite side of the outer race 36. In Fig. 9, the shank of the control head 22 is provided with an integral collar 323 having arcuate sides to form races for two rows of balls which co-operate with arcuate section race surfaces provided at the ends of an annular cavity 35 provided in the outer race 37.

Fig. 10 shows a portion of the propeller hub with a hub extracting device in position.

The hub withdrawing device comprises a plate 331 having an opening 392 through which a screw bolt 303 is passed, the said screw bolt being screwed into one of the lugs 251 after removal of the screw bolts 25 from the respective lugs 251. As shown in Figure 10, the rear end of the part 1 of the propeller hub is provided with a cylindrical boss sea having a series of axial slots 305 in its periphery, which are adapted to be engaged by teeth provided on an arm 3% offset from the plate Sill. The plate S il-l is also provided with a screw-threaded opening 3J7, which is so located that it is in alignment with the propeller shaft 8 when the plate 301 is connected to the lug 251. by means of the bolt 303 and the teeth of the arm 3% are in engagenient with the slots 305. A screw 308 is screwed into the opening 307.

In order to remove the propeller hub from the shaft 8, the nut 16 is removed and the hub withdrawing device is placed in position as shown in Figure 10. The screw 308 is then turned so as to bear against the end of the propeller shaft 8 and force the plate 301 axially away in the rearward direction from the propeller shaft, the propeller hub 14, 15 being thereby withdrawn from the propeller shaft by means of the bolt 13 screwed into the lug 251.

In the embodiment shown in Figs. 11 to 16, the propeller shaft 81 is hollow and extends through the stern of the ship, being supported outside the hull by means of a stern bracket 911. The rear end of the shaft 81 is provided with an integral flange 82 which is bolted to the forward wall 83 of a hollow two-part propeller hub 84, 85. A deeply dished flange member 86 is keyed on the forward end of the shaft 81, the said member being bolted to the enlarged rear end 87 of a sleeve 88 which thus constitutes an extension of the propeller shaft 81. The sleeve 88 extends axially into the casing of the main thrust bearing 43 and is freely rotatable and axially slidable in bearing 42 in the casing of the thrust hearing. The sleeve 88 is provided inside the casing of the thrust bearing 43 with an integral thrust collar 89 which co-operates with thrust bearing elements 44, 45 inside the thrust hearing 43.

The thrust bearing 43 is displaceable fore and aft of the ship, being provided on its underside with a guide 46 which is slidable in a fixed guide 47 mounted in the hull of the ship. The thrust bearing 43 is adjustable in the fore and aft direction of the ship by means of a hydraulic gear comprising a cylinder 50 within which a piston 51 is slidable, the said piston being provided with a piston rod 52 which is connected to a pin 49 fixed on a lug 48 integral with the casing of the thrust bearing 43. The piston 51 is displaceable within the cylinder 50 under the action of oil under pressure which is admitted to the cylinder 50 through pipes 53, 54, so that by placing one side or the other of the piston 51 under oil pressure it displaces the thrust bearing 43 towards or away from the stern of the ship, producing a corresponding axial displacement of the propeller shaft. The sleeve 88 is provided with internal spline teeth 90 which engage corresponding spline teeth 91 on a hollow shaft 92 which is driven by the shaft 93 of the main engine of the ship, the arrangement being such that the rotary motion of the shaft 93 is transmitted to the sleeve 88 to rotate the propeller shaft while allowing the thrust bearing 43, the sleeve 88 and the propeller shaft to be displaced axially.

The propeller is provided with three blades 18 the pivots 181 of which extend through bearing openings in the propeller hub 84, 85 into the interior of the hub. As shown in Figs. 12 and 15, each blade pivot 181 comprises a cylindrical portion 182 of larger diameter, an inwardly tapering portion 183 and a cylindrical portion 184 of smaller diameter, the bearing openings in the propeller hub being correspondingly shaped. Each blade pivot 181 has an integral flange 185 at its outer end which bears against a ball thrust bearing 186 located at the bottom of a recess in the propeller hub within which the flange 185 is accommodated. At its inner end, adjacent the cylindrical portion 184, each blade pivot is provided with an integral circular flange 29 which is in bearing contact with the Wall of the propeller hub surrounding the inner end of the opening in which the blade pivot is inserted.

Each blade pivot 181 is provided with an axial opening to receive a bearing stud 187 around which the blade pivot is freely rotatable, the bearing studs 187 of the three blade pivots being integral with a central hub 188 having an opening therein extending coaxially with the axis of rotation of the propeller hub. The two parts 84, of the propeller hub are secured to one another by means of screw bolts 253, the joint between the said parts extending in a plane containing the axes of rotation of the blade pivots.

The blades 18 are adjusted by means of links 19 which are connected to pivot pins 21 on the arms 411 of a control head 221 and to crank pins 20 on the flanges 29 of the respective blade pivots 181. The control head 221 comprises a boss 224 which is secured by means of a nut 223 to the rear end of a rod 41 extending axially through the propeller hub and through the propeller shaft 81 into the hull of the ship, the said rod passing freely through the opening in the boss 188 which connects the studs 187 to one another. The forward end of the rod 41 is located in the enlarged end 87 of the sleeve 88 and is provided with a screw-threaded portion 503 which is screwed into a screw-threaded bore in the end of a shaft 412 which extends through the hollow shaft 92. The forward end of the shaft 81 is provided with a packing gland 500 for sealing the rod 41 at the point where it passes out of the hollow shaft 81. The flange 501 of the follower of the gland 500 is provided with worm teeth 502 to form a worm wheel which co-operates with worms 504 integral with shafts 505, the flange member 86 and the end 87 of the sleeve 88 being provided with recesses, as shown in Figure 14, for the accommodation of the worms 504, and with bores for rotatably supporting the shafts 505, the outer ends of the said bores being enlarged to accommodate driving heads 506 integral with the shafts 505. The driving heads 506 are provided with square-section recesses 507 for the reception of a key, so that the gland 500 can be tightened up from the outside by rotating the worms 504.

The shaft 412 is provided with an integral thrust collar 413 which bears against one side of an annular rib 414 on the inner Wall of the shaft 92. A thrust sleeve 415 is keyed on the reduced forward end of the shaft 412, the said thrust sleeve bearing against the other side of the annular rib 414. In order to enable the thrust sleeve 415 to be removed from the end of the shaft 412, a radial slot is provided in the shaft 92 through which an extracting wedge 416 for the removal of the sleeve 415 from the shaft 412 can be inserted. The Wedge 416 is freely slidable in the said slot and, when driven in, bears against the end of the shaft 412 and against a projection 417 on the inner wall of the sleeve 415, thereby forcing the sleeve 415 off the shaft 412. By means of the thrust collar 413 and the thrust sleeve 415, which bear against the opposite sides of the rib 414, the shaft 412, the rod .41 and the control head 224 are prevented from being axially displaced with respect to the thrust bearing 43. The hub 188 serves for guiding the rod 41 within the propeller hub and the boss 224 of the control head is provided with a flat guiding surface 225 which co-operates with a corresponding guiding surface 226 on the hub cap 227 which closes the rear end of the propeller hub.

The arms 411 of the control head are connected by means of long bolts 38 to a flange 391 integral with a bearing sleeve 39 which is interposed between the liner 40 of the propeller shaft 81 and a lignurn vitae bearing tube 392 in the hub of the stern bracket 911.

When the blades 18 are positioned for driving the ship forwardly the propeller hub is in its extreme forward position, as shown in Fig. 12, the pivot pins 21 on the control head 221 being offset laterally from the axes of the blade pivots and the crank pins 20 being so located on the flanges 29 of the blade pivots that the links 19 extend perpendicularly to the axis of the propeller shaft, as in the case of the embodiment described with reference .to Figs. 1-4. When the main thrust bearing 43 is displaced rearwardly the propeller shaft is displaced axially and rearwardly, together with the propeller hub 84, 8S and the blades 18 relatively to the control head 221, which is fixed axially with respect to the hull of the ship but rotates with the propeller hub and the blades owing to the cooperation of the fiat guiding surfaces 225, 226. When the ship is under way the major part of the power required to produce the axial displacement of the propeller shaft is provided by the wake current, as before, the location of the pivots 21 and the crank pins 20 being such as to allow the propeller shaft, together with the hub 84, 85 and the blades to be displaced rearwardly by the thrust produced on the blades by the wake current, as in the embodiment described with reference to Figs. 1-4. The blades are adjusted angularly to set them into the full astern and feathered positions in the same manner as that of the embodiment illustrated in Figs. 1-4, the links 19 being displaced into the position shown in Fig. 2 when the blades are adjusted for driving the ship rearwardly and for feathering them. Likewise the blades are returned to the full-ahead position in the manner described with reference to Figs. 1-4.

I claim:

1. A reversible screw propeller installation for ships, comprising a main thrust bearing displaceable in the fore and aft direction of the ship, an adjusting device connected to said thrust bearing to eflect the fore and aft displacement of the thrust bearing and to retain it in its adjusted position, a propeller shaft connected to the main thrust hearing and displaceable axially in the fore and aft direction therewith, said propeller shaft extending through the stern of the ship, a screw propeller aggregate comprising a hollow hub fixed to the propeller shaft outside the hull of the ship and having circumferentially spaced bearing openings in the wall thereof, blades mounted on the hub, said blades having pivots which extend through said openings into the hub, and means for effecting angular adjustment of the blades, including a control head within the hub, means connected to the control head and to the hull of the ship to prevent displacement of the control head in the fore and aft direction of the ship, driving means on said control head and propeller aggregate to constrain the control head to rotate with the propeller aggregate, flanges integral with the blade pivots inside the hub, crank pins on said flanges, pivot pins on the control head offset laterally from the axes of rotation of the blade pivots and links connected to said pivot pins and to the crank pins on the flanges of the respective blade pivots to extend perpendicularly to the axis of the propeller shaft when the said hub is in its extreme forward position to set the blades to the position for driving the ship in the full ahead direction, so as to rotate the blade pivots to adjust the blades for driving the ship astern on the propeller shaft and propeller aggregate being displaced rearwardly with respect to the control head and to rotate the blade pivots to restore the blades to the position for driving the ship forwardly on the propeller shaft being displaced forwardly again.

2. A reversible screw propeller installation for ships, comprising a main thrust bearing displaceable in the fore and aft direction of the ship, an adjusting device connected to said thrust bearing to effect the fore and aft displacement of the thrust bearing and to retain it in its adjusted position, a propeller shaft connected to the main thrust bearing and displaceable axially in the fore and aft direction therewith, said propeller shaft extending through the stern of the ship, a screw propeller aggregate comprising a hollow hub fixed to the propeller shaft outside the hull of the ship and having circumferentially spaced bearing openings in the wall thereof, with bearing surfaces on the inner side of said wall surrounding said openings, blades mounted on the hub, said blades having pivots which extend through said openings into the hub, flanges integral with the blade pivots inside the hub and co-operating with said bearing surfaces, a control head within the hub, means connected to the control head and to the hull of the ship to prevent displacement of the control head in the fore and aft direction of the ship, said control head having bearing surfaces for co-operation with said flanges of the blade pivots to constrain the control head to rotate with the propeller aggregate, crank pins on said flanges, pivot pins on the control head olfset laterally from the axes of rotation of the blade pivots and links connected to said pivot pins and to the crank pins on the flanges of the respective blade pivots to extend perpendicularly to the axis of the propeller shaft when the said hub is in its extreme forward position to set the blades to the position for driving the ship in the full ahead direction, so as to rotate the blade pivots to adjust the blades for driving the ship astern on the propeller shaft and propeller aggregate being displaced rearwardly with respect to the control head and to rotate the blade pivots to restore the blades to the position for driving the ship forwardly on the propeller shaft being displaced forwardly again.

3. A reversible screw propeller installation as defined in claim 1, wherein the blade pivots and the said bearing openings in the wall of the hub are tapered inwardly.

4. A screw propeller installation as defined in claim 1, wherein the blade pivots and the said openings in the wall of the hub each comprise a cylindrical portion of large diameter, a cylindrical portion of smaller diameter with the flange of the blade pivot adjacent the inner end of the cylindrical portion of smaller diameter, and an inwardly tapered portion adjacent said cylindrical portions of the blade pivot and bearing opening.

5. A reversible screw propeller installation as defined in claim 1, wherein the means to prevent displacement of the control head in the fore and aft direction of the ship comprise a retaining sleeve extending into the propeller hub and secured to the stern of the ship and a roller thrust bearing mounted in said sleeve and on the control head.

References Cited in the file of this patent UNITED STATES PATENTS 602,902 Foster Apr. 26, 1898 612,618 Sintz Oct. 18, 1898 713,441 Irwin Nov. 11, 1902 789,999 Patrick May 16, 1905 811,287 Gray Jan. 30, 1906 1,024,339 Johnson Apr. 23, 1912 1,181,458 Iskels May 2, 1916 1,656,019 Roberts Jan. 10, 1928 

